Wiper device control method, wiper device and motor with speed reduction mechanism

ABSTRACT

A wiper device, wherein a sensor magnet  41  fitted to an output shaft  34  is so formed that when wiper arms  1   a,    1   b  are positioned at upper reversal positions B relative to an origin position O, both hole ICs  37   a,    37   b  are opposed to an S-pole and when the wiper arms  1   a,    1   b  are positioned at lower reversal positions A relative to the origin point O, at least one of the hole ICs  37   a,    37   b  is opposed to an N-pole, and when the wiper arms  1   a,    1   b  are abnormally stopped, the sensor magnet  41  determines at the time of re-starting whether the wiper arms  1   a,    1   b  are positioned at the lower reversal positions A or at the upper reversal positions B relative to the origin position O and always starts the wiper arms  1   a,    1   b  toward the origin position O, whereby the positions of the wiper arms can be accurately detected by two hole ICs  37   a,    37   b  and, after re-setting position data by re-starting the wiper arms toward the origin position O, the sensor magnet  41  performs a normal control.

TECHNICAL FIELD

This invention relates to an electric motor to be used for a wiperdevice of a vehicle such as an automobile, a method of controlling suchan electric motor and a method of controlling a wiper device of avehicle such as an automobile. More particularly, the present inventionrelates to a technique of controlling a wiper device using a reversibleelectric motor as drive source.

BACKGROUND ART

An electric motor energized by a power source such as a battery loadedon the vehicle is normally used as drive source of a wiper device of avehicle such as an automobile. Such an electric motor is equipped with aspeed reduction mechanism for reducing the number of revolutions of theoutput shaft thereof to a predetermined number of revolutions, the motoris unitized as an electric motor with the speed reduction mechanism. Oneor two such motor units are used for a wiper device and a wiper arm isdriven by the drive source of the motor unit or units to swing betweenan upper reversal position and a lower reversal position where it turnsaround. When a single motor unit is used, the wiper arm at the driver'sseat and the one at the passenger seat are combined by a link and drivensynchronously. When two motor units are used, the wiper arm at thedriver's seat and the one at the passenger seat are connected to therespective motor units and driven synchronously, while detecting therevolutions of the armature shaft and those of the output shaft.

Meanwhile, the space for installing a wiper system has been reduced yearby year as a result of the increase in the dimensions of the engine andalso in the master power of the brake. As a result, there have beenmarketed a system that can drive a wiper within a small space byreversing the motion of the motor by less than 180° in order to reducethe operating area of the link to less than a half of the ordinary area.Since such a motor reversing system can reverse the moving direction ofthe wiper at any desired position within the wiping angle of the wiper,it is possible to define the lower reversal position and set a wiperstoring space below the defined position. Many high quality carscurrently adopt the system and are provided with such a wiper storingfeature.

When reversing the motion of the motor of a wiper system, it isnecessary to detect the wiper arm position in order to reverse themotion of the motor at a desired position of the wiper arm. The wiperarm position is detected by adding/subtracting the number of pulsesgenerated by a pulse generator whose operation is interlocked with therotary motion of the motor. A multi-polar magnet is fitted to the rotaryshaft of the motor and a sensor typically comprising Hall ICs isarranged vis-à-vis the magnet in order to detect the polar change due tothe rotation of the rotary shaft and to output a pulse signal. The pulsecount is reset at a point (origin position) that operates as referenceposition for the rotary position of the output shaft of the motor unitin order to prevent discrepancies of pulses. A magnet is also fitted tothe output shaft and a corresponding sensor is arranged in such a waythat the sensor outputs a reference signal when a magnetic pole passesby a predetermined position.

The rotary angle of the motor from the reference position is computed byadding/subtracting the number of pulses after the reset so that it ispossible to detect the current wiper arm position by taking thereduction ratio and the link ratio into consideration. It is alsopossible to detect the rotary speed of the moving wiper arm from thecycle period of pulses generated due to the rotary motion of the motor.The motor control system is provided with a reversing circuit which maytypically be an H-bridge circuit that comprises FETs and a control meanssuch as a CPU for controlling the rotary speed and the rotary angle ofthe motor so that the operation of driving the motor is controlledaccording to the wiper arm position and the rotary speed of the wiperarm.

In such a known wiper system that is adapted to be driven to operate bya reversible motor, if an abnormal condition arises because of a powershut down or some reason on the way of a wiping operation, the pulsecount that indicates the wiper arm position can be lost to make itimpossible to accurately recognize the wiper arm position when the wipersystem is restarted. Then, the wiper blade can overrun to collide withthe corresponding pillar at an end of the windshield and/or a componentof the reduction mechanism or the link mechanism can hit the mechanicalstopper arranged in the motor unit.

When it snows, snow flakes can be accumulated on the wiper blade so thatit is sometimes very difficult to start driving the blade and move itfrom the stored position. Then, the car driver may often have to drivethe blade to reciprocate between the stored position and the lowerreversal position manually or automatically in order to activate thewiper device. However, when the motor is operated for forward rotationand reverse rotation repeatedly, the pulse count that indicates thewiper arm position can become to show discrepancies. Then, asdiscrepancies are accumulated, the operation of the blade can becomeunstable.

In the above-described wiper system, a sensor for detecting the rotaryposition of the output shaft is arranged not only at the origin positionbut also at the upper and lower reversal positions and at the storedposition in order to detect the wiper arm position at a number oflocations for the purpose of stabilizing the operation of the blade.Thus, an arrangement is made to quickly recognize the wiper arm positionand prevent it from overrunning or otherwise operating unstably if thesystem is restarted without recognizing the position at which the wiperarm is stopped or if the pulse count gives rise to discrepancies andthey are accumulated. However, with such an arrangement, since it isnecessary to install at least four expensive sensors for a single motor,there is a problem that a unit price increases and it causes a costrise.

An object of the present invention is to provide a wiper device controlmethod, and the like that can reliably detect the wiper arm positionwith a small number of sensors.

DISCLOSURE OF THE INVENTION

A method for controlling a wiper device of the present invention,detecting the position of a wiper arm on the basis of the state wherethe wiper arm is positioned at a reference position, and driving thewiper arm to reciprocate between an upper reversal position and a lowerreversal position for a wiping operation, wherein, when the wiper armstops between the upper reversal position and the lower reversalposition in operation, it is always started to move toward the referenceposition at the time of restarting.

Thus, according to the invention, if the wiper arm abnormally stopsbetween the upper reversal position and the lower reversal positionbecause of a power shut down or some other reason, it is forced tofirstly pass the reference position without fail at the time ofrestarting. Therefore, it is possible to accurately grasp the wiper armposition.

Preferably, a stored position of the wiper arm is arranged below thelower reversal position in the wiper device and when the wiper arm stopsat a position other than the stored position, the wiper arm is alwaysstarted to move toward the reference position at the time of restarting.

In another aspect of the present invention, there is provided a wiperdevice adapted to be driven by an electric motor with a speed reductionmechanism including a motor main body having a rotary shaft and a speedreduction mechanism for reducing the number of revolutions of the rotaryshaft and transmitting the revolutions of the rotary shaft to an outputshaft, comprising: a wiper arm connected to the output shaft and adaptedto reciprocate between an upper reversal position and a lower reversalposition for a wiping operation; a first magnetism detection elementarranged so as to be located vis-à-vis a predetermined position of theoutput shaft when the wiper arm is at a reference position; a secondmagnetism detection element arranged at a position separated from thefirst magnetism detection element by a predetermined angle; and a sensormagnet arranged at the output shaft and having a first magnetic pole anda second magnetic pole arranged in a peripheral direction and showingdifferent polarities, both the first and second magnetism detectionelements being located vis-à-vis the second magnetic pole when the wiperarm is at the side of the upper reversal position relative to thereference position, at least either the first magnetism detectionelement or the second magnetism detection element being locatedvis-à-vis the first magnetic pole when the wiper arm is at the side ofthe lower reversal position relative to the reference position.

Thus, according to the invention, it is possible to judge if the wiperarm is at the side of the upper reversal position or at the side of thelower reversal position relative to the reference position bydetermining the polarity of the first magnetic pole and that of thesecond magnetic pole by means of the first and second magnetismdetection elements. As a result, if the wiper arm abnormally stopsbetween the upper reversal position and the lower reversal positionbecause of a power shut down or some other reason, it is possible toforce the wiper arm to firstly pass the reference position without failat the time of restarting.

In the wiper device according to the invention, preferably, the firstmagnetism detection element may be located vis-à-vis the boundary of thefirst magnetic pole and the second magnetic pole when the wiper armpasses reference position. In the wiper device according to theinvention, preferably, both the first magnetism detection element andthe second magnetism detection element may be located vis-à-vis thefirst magnetic pole when the wiper arm is at the lower reversalposition. In the wiper device according to the invention, preferably,the stored position of a wiper arm may be arranged below the lowerreversal position and the first magnetism detection element may belocated vis-à-vis the first magnetic pole and the second magnetismdetection element may be located vis-à-vis the second magnetic pole whenthe wiper arm is at the stored position.

In the wiper device according to the invention, preferably, when thewiper arm stops between the upper reversal position and the lowerreversal position in operation, it is always started to move toward thereference position at the time of restarting. In the wiper deviceaccording to the invention, preferably, when the wiper arm stops at aposition other than the stored position, the wiper arm is always startedto move toward the reference position at the time of restarting. Withany of the above-described arrangements, when the wiper arm abnormallystops because of a power shut down or some other reason, the wiper armis forced to firstly pass the reference position without fail at thetime of restarting. Therefore, it is possible to accurately grasp thewiper arm position by means of the two magnetism detection elements.

Preferably, the wiper device according to the invention furthercomprises a sensor for detecting the rotary angle of the rotary shaft,which sensor starts detecting the rotary angle of the rotary shaft atthe time when the wiper arm is positioned at the reference position.

In still another aspect of the invention, there is provided an electricmotor with a speed reduction mechanism including a motor main bodyhaving a rotary shaft and a speed reduction mechanism for reducing thenumber of revolutions of the rotary shaft and transmits the revolutionsto an output shaft, comprising: a first magnetism detection elementlocated at a reference position arranged vis-à-vis a predetermined stateof the output shaft when the output shaft is at a predeterminedposition; a second magnetism detection element arranged at a positionseparated from the first magnetism detection element by a predeterminedangle; and a sensor magnet arranged at the output shaft and having afirst magnetic pole and a second magnetic pole arranged in a peripheraldirection and showing different polarities, both the first and secondmagnetism detection elements being located vis-à-vis the second magneticpole when the output shaft is at one side relative to the referenceposition, at least either the first magnetism detection element or thesecond magnetism detection element being located vis-à-vis the firstmagnetic pole when the output shaft is at the other side to thereference position.

Thus, according to the invention, it is possible to judge if thepredetermined position of the output shaft is either side of rotatingdirection relative to the reference position as the polarity of thefirst magnetic pole and that of the second magnetic pole are determinedby means of the first and second magnetism detection elements. As aresult, if the motor abnormally stops because of a power shut down orsome other reason, it is possible to force it to start in such a waythat the predetermined position of the output shaft thereof comes to belocated vis-à-vis the reference position with the smallest rotary angle.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm toreciprocate between an upper reversal position and a lower reversalposition for a wiping operation, wherein a reference position and alower limit position for mechanically restricting the operation of thewiper arm are arranged respectively between the upper reversal positionand the lower reversal position and below a stored position and, whenthe wiper arm stops in operation, it is always started to move towardthe lower limit position at the time of restarting.

Thus, according to the invention, if the wiper arm abnormally stops atany position, it is forced to pass the reference position or get to thelower limit position without fail in its one way movement afterrestarting. Therefore, it is possible to accurately grasp the wiper armposition at the time of restarting by detecting the passage through thereference position or the arrival to the lower limit position of thewiper arm at the reference position or the lower limit position. Forexample, in a control system where the wiper arm is driven by anelectric motor and the wiper arm position is detected by means of thecount value of the pulse signal output as a result of the rotary motionof the motor to control the operation of the wiper arm, the passagethrough the reference position of the wiper arm is detected by a sensor.On the other hand, the arrival to the lower limit position gives rise tomechanical restrictions and the count value of the pulse signal at thattime shows a predetermined known value. In other words, with the abovedescribed control method, the position of the wiper arm at the time ofrestarting can be grasped by means of a single sensor that is arrangedat the reference position.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm toreciprocate between an upper reversal position and a lower reversalposition for a wiping operation, wherein a reference position, a storedposition for holding the wiper arm at rest when the wiper arm is stoppedand a lower limit position for mechanically restricting the operation ofthe wiper arm are arranged respectively between the upper reversalposition and the lower reversal position, below the lower reversalposition and below the stored position and, when the wiper arm stopsbetween the upper reversal position and the reference position inoperation, it is always started to move toward the reference position atthe time of restarting but, when the wiper arm stops between thereference position and the stored position in operation, it is startedto move either toward the reference position or toward the lower limitposition at the time of restarting.

Thus, according to the invention, when the wiper arm stops between theupper reversal position and the reference position in operation, it isalways started to move toward the reference position at the time ofrestarting. With this arrangement, the wiper arm is forced to pass thereference position without fail in its one way movement afterrestarting. When the wiper arm stops between the reference position andthe stored position in operation, it is started to move either towardthe reference position or toward the lower limit position at the time ofrestarting. With this arrangement, the wiper arm is forced to pass thereference position or get to the lower limit position without fail inits one way movement after restarting. Since it is possible toaccurately grasp the wiper arm position at the reference position andthe lower limit position as described above, the wiper arm position canbe grasped at the time of restarting by means of a single sensorarranged at the reference position by the above control method.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm toreciprocate between an upper reversal position and a lower reversalposition for a wiping operation, wherein a stored position for holdingthe wiper arm at rest when the wiper device is stopped and a lower limitposition for mechanically restricting the operation of the wiper arm arearranged respectively below the lower reversal position and below thestored position and, when the wiper arm is driven to reciprocate betweenthe lower reversal position and the stored position, it is moved to thelower limit position for operation in each go and return cycle.

Thus, according to the invention, when the wiper arm is driven toreciprocate between the lower reversal position and the stored position,it is moved to the lower limit position for operation in each go andreturn cycle. Since it is possible to accurately grasp the wiper armposition at the lower limit position as described above, the wiper armposition can be grasped in each go and return cycle by the above controlmethod.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm toreciprocate between an upper reversal position and a lower reversalposition for a wiping operation, wherein a reference position, a storedposition for holding the wiper arm at rest when the wiper device isstopped and a lower limit position for mechanically restricting theoperation of the wiper arm are arranged respectively between the upperreversal position and the lower reversal position, below the lowerreversal position and below the stored position and, when the wiper armis driven to reciprocate between the lower reversal position and thestored position and if the wiper arm is driven toward the side of thereference position beyond the lower limit position, it is moved to thelower limit position.

Thus, according to the invention, when the wiper arm is driven toreciprocate between the lower reversal position and the stored positionand if the wiper arm is driven toward the side of the reference positionbeyond the lower limit position, it is moved to the lower limitposition. In other words, if the wiper arm that is supposed toreciprocate between the lower reversal position and the stored positionis driven to go beyond the lower reversal position, it is highlypossible that the wiper arm position is not accurately grasped.Therefore, if such is the case, the wiper arm is driven to move to thelower limit position once in the subsequent operation. Since it ispossible to accurately grasp the wiper arm position at the lower limitposition as described above, the wiper arm position can be graspedaccurately and the positional displacement can be dissolved by the abovecontrol method.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm device bymeans of a motor to reciprocate between an upper reversal position and alower reversal position for a wiping operation and controlling theoperation of the wiper device by detecting the wiper arm position bymeans of the count value of the pulse signal output as a result of therotary motion of the motor, wherein a reference position for resettingthe count value of the pulse signal to a reference value, a storedposition for holding the wiper arm at rest when the wiper device isstopped and a lower limit position for mechanically restricting theoperation of the wiper arm and causing the count value of the pulsesignal to show a predetermined value are arranged respectively betweenthe upper reversal position and the lower reversal position, below thelower reversal position and below the stored position but, when thewiper arm stops in operation between the upper reversal position and thereference position, it is always started to move toward the referenceposition at the time of restarting and the count value of the pulsesignal is reset to the reference value as the wiper arm passes thereference position and, when the wiper arm stops in operation betweenthe reference position and the stored position, it is started eithertoward the reference position or the lower limit position at the time ofrestarting and the count value of the pulse signal is reset to thereference value or the predetermined value as the wiper arm passes thereference position or arrives at the lower limit position, whicheverappropriate.

Thus, according to the invention, when the wiper arm stops between theupper reversal position and the reference position, it is started tomove toward the reference position. As a result, the wiper arm passesthe reference position thereafter in its one way movement without failand the count value of the pulse signal is reset to the reference valueso that it is possible to accurately grasp the position of the wiperarm. When, on the other hand, the wiper arm stops between the referenceposition and the stored position, it is started to move toward thereference position or the lower limit position at the time ofrestarting. As a result, the wiper arm passes the reference position orarrives at the lower limit position thereafter in its one way movementwithout fail and the count value of the pulse signal is reset to thereference value or the predetermined value, whichever appropriate, sothat it is possible to accurately grasp the position of the wiper arm.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm device bymeans of a motor to reciprocate between an upper reversal position and alower reversal position for a wiping operation and controlling theoperation of the wiper device by detecting the wiper arm position bymeans of the count value of the pulse signal output as a result of therotary motion of the motor, wherein a reference position for resettingthe count value of the pulse signal to a reference value, a storedposition for holding the wiper arm at rest when the wiper device isstopped and a lower limit position for mechanically restricting theoperation of the wiper arm and causing the count value of the pulsesignal to show a predetermined value are arranged respectively betweenthe upper reversal position and the lower reversal position, below thelower reversal position and below the stored position and, when thewiper arm is driven to reciprocate between the lower reversal positionand the stored position, it is moved to the lower limit position foroperation in each go and return cycle and the count value of the pulsesignal is reset to the predetermined value in response to the arrival ofthe wiper arm to the lower limit position.

Thus, according to the invention, when the wiper arm is driven toreciprocate between the lower reversal position and the stored position,it is moved to the lower limit position for operation in each go andreturn cycle. It is grasped that the count value of the pulse signalthat indicates the wiper arm position agrees with a predetermined valueat the lower limit position. Thus, the wiper arm position can be graspedin each go and return cycle by means of the above control method.

In still another aspect of the present invention, there is provided amethod for controlling a wiper device, driving a wiper arm by means of amotor to reciprocate between an upper reversal position and a lowerreversal position for a wiping operation and controlling the operationof the wiper device by detecting the wiper arm position by means of thecount value of the pulse signal output as a result of the rotary motionof the motor, wherein a reference position for resetting the count valueof the pulse signal to a reference value, a stored position for holdingthe wiper arm at rest when the wiper arm is stopped and a lower limitposition for mechanically restricting the operation of the wiper arm andcausing the count value of the pulse signal to show a predeterminedvalue are arranged respectively between the upper reversal position andthe lower reversal position, below the lower reversal position and belowthe stored position and, when the wiper arm is driven to reciprocatebetween the lower reversal position and the stored position and if thecount value of the pulse signal shows a value indicating as if the wiperarm were positioned at the side of the reference position beyond thelower limit position, the wiper arm is moved to the lower limit positionand the count value of the pulse signal is reset to the predeterminedvalue in response to the arrival of the wiper arm to the lower limitposition.

Thus, according to the invention, when the wiper arm is driven toreciprocate between the lower reversal position and the stored positionand if the count value of the pulse signal shows a value indicating asif the wiper arm were positioned at the side of the reference positionbeyond the lower limit position, the wiper arm is moved to the lowerlimit position. If the pulse count value exceeds the value for the lowerreversal position, although the wiper arm is supposed to be driven toreciprocate between the lower reversal position and the stored position,it is highly possible that the wiper arm position is not accuratelygrasped. Therefore, if such is the case, the wiper arm is driven to moveto the lower limit position once in the subsequent operation. Since itis grasped that the count value of the pulse signal that indicates theposition of the wiper arm shows a predetermined value at the lower limitposition, the wiper arm position can be grasped accurately and thepositional displacement can be dissolved by means of the above controlmethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic illustration of a wiper device using electric motorswith a speed reduction mechanism of an embodiment of the presentinvention as drive source;

FIG. 2 is a schematic cross sectional view of the electric motors ofFIG. 1;

FIG. 3 is a partially cut out cross sectional view of the worm gear ofFIG. 2, illustrating the engagement thereof;

FIG. 4 is a schematic illustration of the positional relationshipbetween the Hall ICs and the sensor magnet;

FIG. 5 is a table illustrating the combinations of magnetic poles thatthe Hall ICs detect respectively at corresponding control points;

FIG. 6 is a schematic cross sectional view of a motor unit that is usedfor a wiper device to which a control method according to the inventionis applicable;

FIG. 7 is a schematic illustration of the inside of the case frame ofthe motor unit of FIG. 6 as viewed from above;

FIG. 8 is a schematic illustration of the inside of the case frame ofthe motor unit similar to FIG. 7 but without the gear in the gear box;

FIG. 9 is a schematic illustration of the configuration of the secondgear of the motor unit of FIG. 6;

FIG. 10 is a schematic illustration of the relationship between themagnet and the Hall ICs and the output signal (motor pulse) of the HallICs;

FIG. 11 is a schematic illustration of the moving range of the wiperblade of the wiper device;

FIG. 12 is a schematic illustration of the positional relationshipbetween the Hall ICs and the magnet;

FIG. 13 is a table illustrating the combinations of magnetic poles thatthe Hall ICs detect respectively at corresponding control points; and

FIG. 14 is a schematic illustration of another example of definition ofa mechanical restricting position.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, an embodiment of the present invention will be described in detailbelow with reference to the accompanying drawings.

FIRST EMBODIMENT

FIG. 1 is schematic illustration of a wiper device using electric motorswith a speed reduction mechanism of a first embodiment of the presentinvention as drive source. FIG. 2 is a schematic cross sectional view ofthe electric motors of FIG. 1. FIG. 3 is a partially cut out crosssectional view of the worm gear of FIG. 2, illustrating the engagementthereof.

The wiper device illustrated in FIG. 1 comprises a wiper arm 1 aswingably arranged at the side of the driver's seat of an automobile anda wiper arm 1 b also swingably arranged at the side of the passengerseat of the automobile. A driver's seat side wiper blade 2 a and apassenger seat side wiper blade 2 b are fitted respectively to the wiperarm 1 a and 1 b. The wiper blades 2 a, 2 b are resiliently held incontact with a windshield 3 by means of spring members and the like (notshown) internally and respectively fitted thereto. The body of theautomobile is provided with two wiper shafts 4 a, 4 b. The wiper arms 1a, 1 b are fitted respectively to the wiper shafts 4 a, 4 b at the basesections thereof.

As each of the wiper blades 2 a, 2 b swings between upper reversalposition A and lower reversal position B and hence in a wiping range 5as indicated by dotted broken lines in FIG. 1, the rain drops or snowflakes adhering to the wiping range of the windshield 3 are wiped away.When the wiper device is at rest, each of the wiper blades 2 a, 2 b ismoved to stored position C that is located below the lower reversalposition A and stored in a storage section 6. The storage section 6 isarranged in the inside of the bonnet (not shown) of the body of theautomobile. As the wiper blades 2 a, 2 b are stored in the storagesection 6, the front view of the automobile is improved for both thedriver and the passenger. An origin position (reference position) O isdefined for each of the wiper blades 2 a, 2 b at a position above thelower reversal position A by about 15°.

The wiper device is provided with two electric motors having respectivespeed reduction mechanisms 7 a, 7 b (to be referred to simply as motors7 a, 7 b hereinafter) for driving the wiper arms 1 a, 1 b to swingrespectively. As shown in FIG. 2, each of the motors 7 a, 7 b has amotor main body 8 and a speed reduction mechanism 9. The motor main body8 has a motor housing 10 that substantially shows a profile of abottomed cylinder. The speed reduction mechanism 9 has a casing 11,which includes a bearing section 11 a, which collectively show acylindrical profile similar to that of the motor housing 10 and havedimensions substantially same as those of the motor housing 10, a gearchamber 11 b and a communication section 11 c. These members are puttogether by means of a fastening member (not shown) in a state where theopen end 10 a of the motor housing 10 and the bearing section 11 a ofthe casing 11 are held in contact with each other.

Two permanent magnets 12, 13 are arranged on the inner peripheralsurface of the motor housing 10 with the opposite magnetic poles thereoffacing each other to produce a magnetic field in the inside of the motorhousing 10. An armature 14 is arranged within the magnetic field in theinside of the motor housing 10. The rotary shaft 15 of the armature 14is rotatably supported by self-aligning type bearings 16, 17. Thebearings 16, 17 are arranged respectively on the bottom 10 b of themotor housing 10 and in the bearing section 11 a.

The armature 14 has an armature core 18 that is provided with aplurality of slots. A copper wire is wound around the armature core 18through the slots to form an armature coil 19. A commutator 29 is fixedto the shaft at the left side of the armature core 18 in FIG. 2. Thecommutator 20 includes a trunk section 20 a, which is made of resin andrigidly fitted to the rotary shaft 15, and a plurality of commutatorsegments 20 b, which is radially arranged on the periphery of the trunksection and insulated each other. The commutator segments 20 b areconnected to the armature coil 19.

A brush holder 21 is arranged in the inside of the bearing section 11 a.Two brushes 22, 23 are fitted to the brush holder 21. The brushes 22, 23are urged toward the commutator segments 20 b and contact the commutatorsegments 20 b in the urged state. A power supply terminal 25 is arrangedin the communication section 11 c and connected to the brushes 22, 23 byway of wires 24. The brushes 22, 23 are supplied with respectivelyelectric currents in opposite directions as an electric current issupplied to the power supply terminal 25 from a control section (notshown).

Since the armature coil 19 is located in a magnetic field, rotary poweris generated in the armature 14 according to the Fleming's left handrule as a rectified electric current is made to flow to the armaturecoil 19 by way of the commutator 20. Thus, the rotary angle, therotating direction and the rotary speed of the rotary shaft 15 can becontrolled by controlling the electric current flowing to the armaturecoil 19.

The rotary shaft 15 projects into the inside of the gear chamber 11 b.The front end section 15 a of the rotary shaft 15 is located near thewall surface 26 of the gear chamber 11 b that is located away from themotor main body 8. As shown in FIG. 3, two worms 27, 28 that arethreaded in opposite directions are formed in the outer peripheralsurface of the rotary shaft 15 at a position located in the inside ofthe gear chamber 11 b. Two worm wheels 29, 30 are arranged in the insideof the gear chamber 11 b so as to be engaged with the worms 27, 28respectively. Thus, the worms 27, 28 and the worm wheels 29, 30constitute a worm gear 31. Pinion gears 32, 33 are arranged so as to berespectively coaxial with the worm wheels 29, 30. The pinion gears 32,33 are engaged with a drive gear 35 that is a rotary body integral withthe output shaft 34 of the speed reduction mechanism 9. Thus, the rotarymotion of the rotary shaft 15 is transmitted to the output shaft 34 at arotary speed that is reduced by the worm gear 31, the pinion gears 32,33 and the drive gear 35.

The output shafts 34 of the motors 7 a, 7 b are mechanically linked tothe respective wiper shafts 4 a, 4 b. The wiper shafts 4 a, 4 b rotateintegrally with the respective output shafts 34. As the rotary shaft 15rotates, the worms 27, 28 are subjected to thrust that acts in the axialdirection of the rotary shaft 15 because of the provision of the wormwheels 29, 30. Since the worms 27, 28 are threaded in oppositedirections, the thrust is made to act in two opposite directions. As aresult, any movement of the rotary shaft 15 in the directions of thethrust is suppressed and hence it is not necessary to arrange any thrustbearing and the like for the rotary shaft 15. While a double reductiongear mechanism formed by the worm gear 31, the pinion gears 32, 33 andthe drive gear 35 is used for the speed reduction mechanism 9 of thisembodiment, the present invention is by no means limited thereto and asingle reduction gear mechanism formed by using only a worm gear or aplanetary gear mechanism may alternatively be used.

A printed circuit board 36 is fitted to the wall surface 26 of thecasing 11 and arranged so as to extend perpendicularly relative to therotary shaft 15. A connection terminal 40 located in the communicationsection 11 c is fitted to the printed circuit board 36. Power issupplied and detection signals are transmitted from a control section(not shown) by way of the connection terminal 40.

Two absolute position detecting Hall ICs 37 a, 37 b and two relativeposition detecting Hall ICs 38, 39 are fitted onto the printed circuitboard 36 respectively as first sensor and second sensor. Hall ICs thatcan detect the type of the magnetic poles each time they are switchedare used for the Hall ICs 37 a, 37 b. In other words, they can determineif the object of detection is the N-pole or the S-pole. While Hall ICsare used for the relative position detecting sensor in this embodiment,the present invention is by no means limited thereto and an opticalencoder realized by using photo-diodes, an infrared sensor or a sensorof some other type may alternatively be used.

A Hall IC is a sensor that transforms a change in the magnetic fieldinto an electric current and emits a pulse signal. The object ofdetection of a Hall IC needs to be a magnet. A ring-shaped sensor magnet41 is attached to the bottom of the drive gear 35 along the outerperipheral surface thereof as object of detection for the absoluteposition detecting Hall ICs 37 a, 37 b. The sensor magnet 41 is adaptedto rotate integrally with the drive gear 35 and magnetized to show twopoles in the sense of rotation thereof. A multi-polar magnet 42 (to bereferred to simply as magnet 42 hereinafter) is fitted to the front end15 a of the rotary shaft 15 as object of detection for the relativeposition detecting Hall ICs 38, 39. The magnet 42 is adapted to rotateintegrally with the rotary shaft 15 and magnetized to show six poles inthe sense of rotation thereof.

FIG. 4 is a schematic illustration of the positional relationshipbetween the Hall ICs 37 a, 37 b and the sensor magnet 41. As shown inFIG. 4, one of the poles (S-pole in the illustrations) of the sensormagnet 41 is made to show a larger angle of magnetization than the otherpole (N-pole in the illustrations). As the drive gear 35 rotates, themagnetic poles that passes in front of the Hall ICs 37 a, 37 b changeaccordingly. As will be described hereinafter, it is so arranged thatthe positions of the wiper arms 1 a, 1 b can be recognized by means ofthe combination of the changes.

On the other hand, the Hall ICs 38, 39 are fitted to the surface of theprinted circuit board 36 at respective positions located vis-à-vis themagnet 42 with their phases shifted by 90° in the sense of rotation ofthe magnet 42. As the rotary shaft 15 rotates and makes a full turn, theHall ICs 38, 39 output respective pulses for six cycle periods. Thepulses are transmitted toward a control section (not shown) by way ofthe connection terminal 40 so that it is possible to detect the rotaryangle of the rotary shaft 15 by counting the pulses. Since the phases ofthe Hall ICs 38, 39 are shifted by 90° from each other, the sequence ofappearance of the pulses transmitted from the Hall ICs 38, 39 variesdepending on the sense of rotation of the rotary shaft 15. In otherwords, it is possible to detect the sense of rotation of the rotaryshaft 15 by seeing the sequence of appearance of the pulses.Furthermore, it is possible to detect the rotary speed of the rotaryshaft 15 by detecting the cycle period of the pulses detected by theHall ICs 38, 39.

Now, the operation of the motor will be described below. As a wiperswitch (not shown) is turned on, electric currents are supplied from thecontrol section to the brushes 22, 23 in opposite directions and anelectric current rectified by the commutator 20 flows to the armaturecoil 19. Rotary power is generated in the armature coil 19 by theelectric current to drive the rotary shaft 15 to rotate. The rotation ofthe rotary shaft 15 is transmitted to the output shaft 34 at a rotaryspeed that is reduced by the worm gear 31, the pinion gears 32, 33 andthe drive gear 35 of the speed reduction mechanism 9. As the outputshaft 34 rotates, the wiper arms 1 a, 1 b fitted to the respective wipershafts 4 a, 4 b swing to operate.

When the wiper arms 1 a, 1 b are at the respective stored positions, theHall ICs 37 a, 37 b respectively face the S-pole and the N-pole of thesensor magnet 41. Then, the detection signal of the Hall ICs 37 a, 37 bwill be “37 a: S, 37 b: N” as shown in FIG. 4(a). As the output shaft 34rotates and the wiper arms 1 a, 1 b get to the respective lower reversalpositions, the Hall IC 37 a also comes to face the N-pole of the of thesensor magnet 41. Then, the detection signal of the Hall ICs 37 a, 37 bwill be “37 a: N, 37 b: N” as shown in FIG. 4(b). When the output shafts34 further rotates and the wiper arms 1 a, 1 b get to the respectiveorigin positions, the magnetic pole that the Hall IC 37 a faces isswitched from the N-pole to the S-pole of the sensor magnet 41. Then,the detection signal of the Hall ICs 37 a, 37 b will be “37 a: N→S, 37b: S” as shown in FIG. 4(c). When the wiper arms 1 a, 1 b get to therespective upper reversal positions, both the Hall ICs 37 a, 37 b facethe S-pole of the sensor magnet 41. Then, the detection signal of theHall ICs 37 a, 37 b will be “37 a: S, 37 b: S” as shown in FIG. 4(d).

On the other hand, when the wiper arms 1 a, 1 b are driven to moverespectively from the upper reversal positions toward the lower reversalpositions and get to the origin positions, the magnetic pole that theHall IC 37 a faces is switched from the S-pole to the N-pole of thesensor magnet 41. At this time, the detection signal of the Hall ICs 37a, 37 b will be “37 a: S N, 37 b: S” as shown in FIG. 4(c). The table ofFIG. 5 summarily illustrates the above described transitions. As shownin FIG. 5, the combinations of magnetic poles as detected by the HallICs 37 a, 37 b at the above described control points differ from eachother and hence it is possible to know the current positions of thewiper arms 1 a, 1 b approximately by identifying the currentcombinations of magnetic poles. Additionally, it is possible to detectthe moving direction of the wiper arms 1 a, 1 b by catching the changeof the magnetic pole or poles when the wiper arms 1 a, 1 b passes theorigin positions. In short, the two Hall ICs 37 a, 37 b can recognizethe wiper arms 1 a, 1 b at four positions. The positions of the magneticpoles including the S-pole and the N-pole of the sensor magnet 41 may beswitched.

Assume here that the power supply is turned off when each of the wiperarms 1 a, 1 b is positioned between the upper reversal position and thelower reversal position. Then, the pulse count of each of the wiper arms1 a, 1 b is erased and the positions of the wiper arms 1 a, 1 b will beunknown when the wiper device is restarted. Then, if the motor is drivento operate once again, the wiper arms can overrun because it is notpossible to accurately grasp the positions of the wiper arms 1 a, 1 b.However, the motor of this embodiment firstly drives the wiper arms 1 a,1 b to move toward the respective origin positions O in order to graspthe current positions of the wiper arms 1 a, 1 b. If the wiper arms 1 a,1 b are positioned respectively between the upper reversal positions andthe origin positions O, the signal from the Hall ICs 37 a, 37 b will be“37 a: S, 37 b: S”. If, on the other hand, the signal from the Hall ICs37 a, 37 b is other than the combination of “37 a: S, 37 b: S”, thewiper arms 1 a, 1 b are positioned respectively at the side of the lowreversal positions relative to the origin positions O.

Therefore, when the signal of the Hall ICs 37 a, 37 b is “37 a: S, 37 b:S”, the wiper arms 1 a, 1 b respectively pass the origin positions Owithout fail if they are driven to move toward the sides of the lowerreversal positions. When, on the other hand, the signal of the Hall ICs37 a, 37 b is other than “37 a: S, 37 b: S”, the wiper arms 1 a, 1 brespectively pass the origin positions O without fail if they are drivento move toward the sides of the upper reversal positions. In otherwords, it is possible to determine the positions of the wiper arms 1 a,1 b relative to the origin positions O by examining the combination ofthe signal from the two Hall ICs 37 a, 37 b. Then, the wiper arms 1 a, 1b pass the respective origin positions O without fail and thereforetheir position can be identified by driving the wiper arms 1 a, 1 b tostart moving toward the origin positions O.

After identifying the positions of the wiper arms 1 a, 1 b at the timewhen they pass the respective origin positions, their movements arecontrolled by the ordinary pulse count process. More specifically, thecontrol section starts counting the pulses of the Hall ICs 38, 39 byusing the origin position O as base point and detects the rotary angleof the output shaft 34 on the basis of the counted number of pulses. Ifthe wiper arms 1 a, 1 b are moving toward the respective upper reversalpositions B, the movement of the arms 1 a, 1 b toward the upper reversalpositions B, that is, the moving directions of the arm 1 a, 1 b aredetected by seeing the sequence of appearance of the pulses transmittedfrom the Hall ICs 38, 39 or the change in the signal from the Hall IC 37a at the origin positions O. Then, the absolute positions of the wiperarms 1 a, 1 b are detected from the rotary angle and the sense ofrotation of the output shaft 34.

As the wiper arms 1 a, 1 b keeps on moving and the predetermined numberof pulses are counted, the control section recognizes that the wiperarms 1 a, 1 b are at the respective upper reversal positions B.Accordingly, the directions of the electric currents being supplied tothe brushes 22, 23 are switched. As the electric currents being suppliedto the brushes 22, 23 are switched, the direction of the rotary powerbeing generated in the armature coil 19 is reversed and the motor startsrotating in the opposite direction. As the rotation of the motor isreversed, the wiper arms 1 a, 1 b switch their moving directions at theupper reversal positions B and start moving toward the lower reversalpositions A.

Thereafter, as the wiper arms 1 a, 1 b pass the respective originpositions O, the signal from the Hall IC 37 a becomes to be S→N and thepulse count of the Hall ICs 38, 39 is reset. Then, the pulse count isrestarted for the movements of the wiper arms 1 a, 1 b toward the lowerreversal positions A and, when a predetermined number of pulses arecounted, the control section recognizes that the wiper arms 1 a, 1 b areat the respective lower reversal positions A. Accordingly, the motorstarts rotating in the opposite direction once again and the wiper arms1 a, 1 b start moving toward the upper reversal positions B. As theabove movements are repeated, the wiper arms 1 a, 1 b swing respectivelybetween the lower reversal positions A and the upper reversal positionsB for wiping operations by the wiper blades 2 a, 2 b.

When the wiper switch (not shown) is turned off and it is detected thatthe wiper arms 1 a, 1 b come to the respective lower reversal positionsA for the first time after the turning-off of the wiper switch, thecontrol section drives the wiper arms 1 a, 1 b to move respectively fromthe lower reversal positions A to the storage sections 6. The pulsecounting operation of the Hall ICs 38, 39 is continued during the abovedescribed movements and, when a predetermined number of pulses arecounted, the control section recognizes that the wiper arms 1 a, 1 barrive at the respective stored positions C and stops the supply ofelectric current to the brushes 22, 23.

Thus, if the wiper arms 1 a, 1 b abnormally stop because of a power shutdown or some other reason, the electric motors of this embodimentoperate in such a way that the wiper arms 1 a, 1 b are forced to firstlypass the respective origin positions O without fail at the time ofrestarting after the abnormal stop. Then, the data are reset when thewiper arms 1 a, 1 b pass the respective origin positions O andsubsequently they are driven to move toward the upper or lower reversalpositions. Thus, it is possible to prevent a situation where it cannotrecognize the current position of the arm at the time of restartingafter the abnormal stop and the wiper arms 1 a, 1 b overrun and hit therespective stoppers from taking place and to realize a smooth restartingoperation. The number of sensors required for the above-describedarrangement is limited to only two, which are the Hall ICs 37 a, 37 b.Thus, it is possible to reduce the number of sensors and themanufacturing cost of the product.

SECOND EMBODIMENT

FIG. 6 is a schematic cross sectional view of a motor unit that is usedfor a wiper device to which a control method according to the inventionis applicable. The motor unit 101 of FIG. 6 is adapted to be used asdrive source of a wiper device of an automobile. When the wiper blade ofthe wiper device (to be referred to simply as blade hereinafter) gets tothe upper and lower reversal positions, the sense of rotation of themotor unit 101 is switched.

The motor unit 101 comprises a motor 102 and a gear box 103. Therotation of the rotary shaft 104 of the motor 102 is reduced in the gearbox 103 and output by way of an output shaft 105. The rotary shaft 104is rotatably borne by a yoke 106 showing a profile of a bottomedcylinder. An armature core 107 around which a coil is wound and acommutator 108 are fitted to the rotary shaft 104. A plurality ofpermanent magnets 109 are rigidly secured to the inner surface of theyoke 106. A feed brush 110 is held in contact with the commutator 108.The speed of the motor 102 (the number of revolutions per unit time) iscontrolled by way of the intensity of the electric current supplied tothe brush 110.

Case frame 111 of the gear box 103 is fitted to the peripheral edge ofthe open end of the yoke 106. FIG. 7 is a schematic illustration of theinside of the case frame 111 of the motor unit of FIG. 6 as viewed fromabove. FIG. 8 is a schematic illustration of the inside of the caseframe 111 of the motor unit similar to FIG. 7 but without the gear inthe gear box 103. The front end of the rotary shaft 104 of the motorunit that projects from the yoke 106 is contained in the case frame 111.Worms 112 a, 112 b are formed at the front end of the rotary shaft 104.The worms 112 a, 112 b are engaged respectively with worm gears 113 a,113 b that are rotatably supported by the case frame 111. Small diameterfirst gears 114 a, 114 b are integrally and coaxially formed with therespective worm gears 113 a, 113 b. The first gears 114 a, 114 b areengaged with a large diameter second gear 115. An output shaft 105 isintegrally fitted to the second gear 115 and rotatably borne by the caseframe 111.

The drive power of the motor 2 is transmitted to the output shaft 105 ata reduced rotary speed by way of the worms 112 a, 112 b, the worm gears113 a, 113 b, the first gears 114 a, 114 b and the second gear 115. Thelink mechanism (not shown) of the wiper device is connected to theoutput shaft 105. As the electric motor 102 is driven to operate, thelink member is by turn driven by way of the output shaft 105 andcooperates with the other link members in an interlocked manner to drivethe wiper arm to move.

Stoppers 121, 122 project from the bottom surface 111 a of the caseframe 111 for the purpose of restricting the rotary angle of the secondgear 115. The second gear 115 is provided with a guide groove 123 thatmatches the stoppers 121, 122. FIG. 9 is a schematic illustration of theconfiguration of the second gear 115. The guide groove 123 is formed toextend along the circumference of the second gear 115 and illustrated asa hatched area in FIG. 9. The stoppers 121, 122 are contained in theguide groove 123. The opposite ends of the guide groove 123 are wallsthat operate as respective rotation restricting sections 124, 125. Asthe second gear 115 rotates and the rotation restricting section 124hits the stopper 121, the blade is mechanically restricted so that itcannot move downward any further. Similarly, as the rotation restrictingsection 125 hits the stopper 122, the blade is mechanically restrictedso that it cannot move upward any further.

A multi-polar magnet 116 (to be referred to simply as magnet 116hereinafter) is fitted to the rotary shaft 104 and Hall ICs 117 arearranged in the case frame 111 so as to face the outer periphery of themagnet 116. FIG. 10 is a schematic illustration of the relationshipbetween the magnet 116 and the Hall ICs 117 and the output signal (motorpulse) of the Hall ICs 117. As shown in FIG. 10, the two Hall ICs 117(117A, 117B) are arranged at positions that form 90° relative to thecenter of the rotary shaft 104. Since the magnet 116 is magnetized toshow six poles, as the rotary shaft 104 rotates and makes a full turn,the Hall ICs 117 output respective pulses for six cycle periods.

As shown at the right side in FIG. 10, the pulse signals output from theHall ICs 117A, 117B show a phase difference of ¼ of a cycle period.Therefore, it is possible to determine the sense of rotation of therotary shaft 104 by detecting the timings of appearance of the pulsesfrom the Hall ICs 117A, 117B so that consequently it is possible todetermine if the wiper arm is moving forward or backward. Additionally,it is possible to detect the rotary speed of the rotary shaft 104 fromthe cycle period of the pulse output of one of the Hall ICs 117A, 117B.The number of revolutions per unit time of the rotary shaft 104 and themoving speed of the wiper blade show a correlation that is determined asa function of the reduction ratio and the working ratio of the link sothat it is possible to computationally determine the moving speed of theblade on the basis of the number of revolutions per unit time of therotary shaft 104.

A ring magnet 118 (to be referred to simply as magnet 118 hereinafter)is fitted to the bottom surface of the second gear 115 for the purposeof detecting the absolute positions of the blade. A printed circuitboard 119 is fitted to the case frame 111 and a Hall IC 120 is arrangedon the printed circuit board 119 and vis-à-vis the magnet 118. Asdescribed above, the crank arm is fitted to the second gear 115 so as torotate by about 180° when the blade is driven to reciprocate for awiping operation. As the second gear 115 rotates and the blade gets to apredetermined origin position O, the Hall IC 120 squarely faces themagnet 118 and an origin position reset signal is output.

Thus, the blade is driven by the motor unit 101 to swing between a lowerreversal position A and an upper reversal position B and operate forwiping away the rain drops or snow flakes adhering the windshield of theautomobile. FIG. 11 is a schematic illustration of the moving range ofthe blade. During the wiping operation, the blade reciprocates betweenthe upper and lower reversal positions A and B, or within the wipingrange hatched in FIG. 11. The blade moves from the lower reversalposition A to the upper reversal position B when the motor is driven toturn forward, whereas it moves from the upper reversal position B to thelower reversal position A when the motor is driven to turn backward.When the wiper is at rest, the blade is moved to a stored position Cthat is located below the lower reversal position A and stored in thestorage section. The storage section is arranged in the inside of thebonnet (not shown) of the body of the automobile.

An origin position (reference position) O is arranged at a positionsubstantially at the middle of the wiping range and slightly close tothe lower reversal position A. An origin position reset signal is outputfrom the Hall IC 120 when the blade is positioned at the origin positionO. FIG. 12 is a schematic illustration of the positional relationshipbetween the Hall IC 120 and the magnet 118. The magnet 118 has two polesas shown in FIG. 12. When the blade comes to the origin position O,there arises a change in the polarities of the magnet 118 (S→N whenforwardly rotating, N→S when backwardly rotating) and an origin positionreset signal is output from the Hall IC 120.

The origin position reset signal is used as a reference signal thatindicates the absolute position of the blade. When an origin positionreset signal is obtained, it is judged that the blade just passes theorigin position O shown in FIG. 11. On the other hand, the motor pulsesfrom the Hall IC 117 are used as signal indicating the relative positionof the blade. The output motor pulses are proportional to the rotaryangle of the rotary shaft 4 and the pulse count value (accumulatednumber) thereof corresponds to the angle by which the rotary shaft 4rotates. Thus, it is possible to know the extent by which the blade hasmoved from the origin position O by resetting the pulse count value toreference value (zero) when an origin position reset signal is obtainedand counting the motor pulses after the resetting.

Meanwhile, a lower limit position X and an upper limit position Y areformed respectively at the outside of the stored position C and at theoutside of the upper reversal position B by the stoppers 121, 122 andthe guide groove 123 as limits of mechanical motion. The lower limitposition X and the upper limit position Y define mechanical limits andhence located at respective positions that are always separated from theorigin position O by predetermined distances (angles). In other words,when the blade gets to the lower limit position X or the upper limitposition Y, the pulse count value from the origin position O alwaysshows a constant value. Therefore, it is possible to use the lower limitposition X and/or the upper limit position Y as position for resettingthe pulse count value just like the origin position O.

In this embodiment of wiper device control method according to theinvention, the lower limit position X is used as pulse count valuecorrecting position in addition to the origin position O. Firstly, whenthe blade is at the stored position C, the Hall IC 120 is locatedvis-à-vis the S-pole of the magnet 118 and hence the detection signal ofthe Hall IC 120 indicates “S” as shown in FIG. 12(a). As the outputshaft 105 is rotated and the blade reaches the lower reversal positionA, the detection signal also indicates “S” as shown in FIG. 12(b). Asthe output shaft 105 is rotated further and the blade reaches the originposition O, the Hall IC 120 gets to the boundary point of the magneticpoles of the magnet 118 so that the detection signal of the Hall IC 120becomes to indicate “S→N” as shown in FIG. 12(c). Further, when theblade exceeds the origin position O, the Hall IC 120 is locatedvis-à-vis the N-pole of the magnet 118 and hence the detection signal ofthe Hall IC 120 indicates “N”. When the blade gets to the upper reversalposition B, the Hall IC 120 is located vis-à-vis the N-pole of themagnet 118 and hence the detection signal of the Hall IC 120 indicates“N” as shown in FIG. 12(d).

On the other hand, when the blade moves from the upper reversal positionB to the lower reversal position A, the detection signal of the Hall IC120 indicates “N” while the blade is moving between the upper reversalposition B and the origin position O but becomes to indicate “N→S” whenthe blade gets to the origin position O. Once the blade moves beyond theorigin position O, the detection signal of the Hall IC 120 be comes toindicate “N”. The detection signal of the Hall IC 120 still indicates“N” when the blade is positioned at the lower reversal position A or atthe stored position C. The table of FIG. 13 summarily illustrates theabove-described transitions. As seen from FIG. 13, it is possible todetect the moving direction of the blade by seeing the change in themagnetic polarity of the magnet 118 when the blade passes the originposition O. It will be appreciated that the site of the S-pole and thatof the N-pole of the magnet 118 may be switched.

Assume here that the power supply switch is turned off when the blade ispositioned between the origin position O and the upper reversal positionB. The signal from the Hall IC 120 indicates “N” when the blade ispositioned between B and O. Thus, if the signal indicates “N” when poweris supplied once again, the blade is positioned in the area between Band O. Therefore, the wiper device of this embodiment firstly drives theblade to move backwardly toward the origin position O in order to graspthe current position of the blade. If the blade is driven to movebackwardly when it is positioned between B and O, it passes the originposition thereafter without fail. In other words, when the motor 102 isdriven to rotate backwardly while the initial signal from the Hall IC120 indicates “N”, it is possible to obtain an origin position resetsignal thereafter without fail. Once the origin position reset signal isobtained, it is possible to accurately grasp the current position of theblade.

Assume now that the power supply switch is turned off when the blade ispositioned at the side of the stored position C relative to the originposition O. The signal from the Hall IC 120 indicates “S” when the bladeis positioned between 0 and C. When the power supply switch is turned ononce again and the signal indicates “S”, the blade is positioned in thearea. As pointed out above, the lower limit position X is also used aspulse count value correcting position in the wiper device of thisembodiment. Therefore, it is possible to reliably grasp the currentposition of the blade when the blade is positioned in the area and themotor is restarted regardless if the motor is driven to rotate forwardlyor backwardly.

If the motor 102 is driven once again to rotate forwardly and the bladethat is positioned between O and C is driven to move forwardly, theblade passes the origin position o thereafter without fail. Therefore,it is possible to accurately grasp the current position of the blade byacquiring an origin position reset signal. If, on the other hand, themotor 102 is driven once again to rotate backwardly and the blade thatis positioned between O and C is driven to move backwardly, the bladegets to the lower limit position X thereafter without fail. The pulsecount value at the lower limit position X is defined to be apredetermined known value. Therefore, it is possible to accurately graspthe current position of the blade by resetting the pulse count value tothis reproduced value.

The wiper device of this embodiment may be so arranged that the pulsecount value is appropriately corrected by using the lower limit positionX so as not to produce any discrepancies due to a repeated reciprocatingmotion when the blade is positioned between the lower reversal positionA and the stored position C. Either of two techniques may be used tocorrect the pulse count value for this purpose. With the firsttechnique, the blade is moved to the lower limit position X each time itis operated to move and the pulse count value is reset to the countvalue of the lower limit position X. While it is possible to accuratelygrasp the position of the blade because the pulse count value is reseteach time with this technique, it accompanies disadvantages includingthat noises and vibrations can be produced because a mechanicalcollision occurs repeatedly and such a repeated collision degrades thedurability of the wiper device.

With the second technique, the pulse count value is reset when largediscrepancies seem to arise in the pulse. In the wiper device of thisembodiment, when an angular deviation occurs to the blade toward thestored position C, the blade eventually gets to the lower limit positionX as the deviation increases and the pulse count value is automaticallycorrected there. Conversely, when an angular deviation occurs to theblade toward the lower reversal position A, the blade eventually gets tothe origin position O as the deviation increases and the pulse countvalue is automatically reset there. However, such a resetting operationat the origin position O is disadvantageous to the wiper device from thecontrol point of view because the blade is driven to move beyond thelower reverse position A.

For this reason, when an angular deviation occurs to the blade towardthe lower reversal position A and the pulse count shows a valuecorresponding to a position located beyond the lower reversal position Aand at the side of the origin position O, it is judged that there arepulse discrepancies and the blade is driven to move to the lower limitposition X. In other words, if the pulse count value indicates aposition beyond the lower reversal position A, although the blade issupposed to be moving between the lower reversal position A and thestored position C, it is safe to judge that pulse discrepancies havetaken place so that the pulse count value is reset at the lower limitposition X.

In this way, with the wiper device of this embodiment, when the bladeabnormally stops because of a power shut down or some other reason, itis possible to reset the pulse count value, utilizing the originposition O or the lower limit position X, when the blade is started tomove once again from the abnormally stopped state. Therefore, the wiperdevice of this embodiment is free from a situation where it cannotrecognize the current position of the blade when the blade is started tomove once again from an abnormally stopped state and an overrun takesplace at the upper reversal position B and hence the blade is started tomove once again very smoothly. Additionally, the pulse discrepanciesthat take place when the blade is moving between the lower reversalposition A and the stored position C can be corrected accurately to makeit possible to drive the blade to reciprocate very smoothly. Only asingle sensor, or a Hall IC 120, is required for the above-describedoperation of correctly driving the blade in the wiper device of thisembodiment. Thus, it is possible to reduce the number of sensors and themanufacturing cost of the product.

The present invention is by no means limited to the above-describedembodiments, which may be modified and altered in various different wayswithout departing from the scope of the invention.

For example, in each of the above described embodiments, an electricmotor according to the invention is applied to a wiper device of anautomobile, the present invention is by no means limited thereto and itcan find applications in the field of other car accessories such aspower windows and also in the field of home electric appliances. Whilethe two wiper arms are driven to move respectively by means of the twodifferent motors 7 a, 7 b in the above described first embodiment, it ispossible to drive the two wiper arms 1 a, 1 b to move by means of asingle electric motor and a link mechanism. While the present inventionis applied to a parallel wiping type wiper device in each of the abovedescribed embodiments, the present invention can also be applied to anopposite type wiper device. It should be noted here that the magneticpoles (N, S) of the ring-shaped sensor magnet 41 of the first embodimentmay be inversely arranged. Then, the magnetic poles detected by the HallICs 37 a, 37 b are opposite to those illustrated in FIGS. 4 and 5.

The setting of mechanically restricting positions is not limited to theuse of stoppers 121, 122 and a guide groove 123 as described above. Forexample, the rotary angle of the second gear 115 may be restricted bythe engagement of a pin that is arranged to project from the case frame111 and a groove that is formed to contain the pin in the second gear115. As shown in FIG. 14, a rotary restricting section 126 forrestricting swing angle is provided in the link mechanism, andaccordingly, a mechanical limit position may be set.

Thus, according to the invention, in a wiper device control method fordetecting the position of the wiper arm, using the state where the armis positioned at the reference position as original position, anddriving the wiper arm to reciprocate between an upper reversal positionand a lower reversal position for a wiping operation, when the wiper armstops between the upper reversal position and the lower reversalposition in operation, it is always started to move toward the referenceposition at the time of restarting. Thus, if the wiper arm abnormallystops between the upper reversal position and the lower reversalposition because of a power shut down or some other reason, it is forcedto firstly pass the reference position without fail at the time ofrestarting. Therefore, it is possible to accurately grasp the wiper armposition. Thus, it is possible to prevent the blade from overrunning andany of the mechanical components of the wiper device from colliding withthe stoppers when the blades are restarted.

According to the invention, a wiper device comprises a sensor magnethaving a first magnetic pole and a second magnetic pole. Both first andsecond magnetism detection elements are located vis-à-vis the secondmagnetic pole (e.g., the S-pole) when a wiper arm is at the side of anupper reversal position relative to a reference position, and at leasteither the first magnetism detection element or the second magnetismdetection element is located vis-à-vis the first magnetic pole (e.g.,the N-pole) when the wiper arm is at the side of a lower reversalposition relative to the reference position. Thus, it is possible tojudge if the wiper arm is at the side of the upper reversal position orat the side of the lower reversal position relative to the referenceposition by determining the polarity of the first magnetic pole and thatof the second magnetic pole by means of the first and second magnetismdetection elements. As a result, if the wiper arm abnormally stopsbetween the upper reversal position and the lower reversal positionbecause of a power shut down or some other reason, it is possible toforce the wiper arm to firstly pass the reference position without failat the time of restarting and to grasp accurately the position of thewiper arm by the two magnetism detection elements. Then, it is possibleto reduce the number of magnetism detection elements and hence the costof manufacturing the device.

According to the invention, in a wiper device control method for drivingthe wiper arm to reciprocate between an upper reversal position and alower reversal position for a wiping operation, a reference position anda lower limit position for mechanically restricting the operation of thewiper arm are arranged respectively between the upper reversal positionand the lower reversal position and below the stored position and, whenthe wiper arm stops in operation, it is always started to move towardthe lower limit position at the time of restarting. Thus, if the wiperarm abnormally stops at any position, it is forced to pass the referenceposition or get to the lower limit position without fail after the timeof restarting. Therefore, it is possible to accurately grasp the wiperarm position at the time of restarting by detecting the passage throughthe reference position or the arrival to the lower limit position of thewiper arm.

For example, in a control system where the wiper arm is driven by anelectric motor and the wiper arm position is detected by means of thecount value of the pulse signal output as a result of the rotary motionof the motor to control the operation of the wiper arm, the passagethrough the reference position of the wiper arm is detected by a sensor.On the other hand, the arrival to the lower limit position gives rise tomechanical restrictions and the count value of the pulse signal at thattime shows a predetermined known value. In other words, with the abovedescribed control method, the position of the wiper arm at the time ofrestarting can be grasped by means of a single sensor that is arrangedat the reference position. Then, it is possible to reduce the number ofsensors to a minimally necessary number and hence the cost ofmanufacturing the device.

1. A method for controlling a wiper device, detecting the position of awiper arm on the basis of the state where the wiper arm is positioned ata reference position, and driving the wiper arm to reciprocate betweenan upper reversal position and a lower reversal position for a wipingoperation, wherein, when the wiper arm stops between the upper reversalposition and the lower reversal position in operation, it is alwaysstarted to move toward the reference position at the time of restarting.2. The method according to claim 1, wherein, a wiper arm stored positionis arranged below the lower reversal position in the wiper device andwhen the wiper arm stops at a position other than the stored position inoperation, the wiper arm is always started to move toward the referenceposition at the time of restarting.
 3. A wiper device adapted to bedriven by an electric motor with a speed reduction mechanism including amotor main body having a rotary shaft and a speed reduction mechanismfor reducing the number of revolutions of the rotary shaft andtransmitting the revolutions of the rotary shaft to an output shaft,comprising: a wiper arm connected to the output shaft and adapted toreciprocate between an upper reversal position and a lower reversalposition for a wiping operation; a first magnetism detection elementarranged so as to be located vis-à-vis a predetermined position of theoutput shaft when the wiper arm is at a reference position; a secondmagnetism detection element arranged at a position separated from thefirst magnetism detection element by a predetermined angle; and a sensormagnet arranged at the output shaft and having a first magnetic pole anda second magnetic pole arranged in a peripheral direction and showingdifferent polarities, both the first and second magnetism detectionelements being located vis-à-vis the second magnetic pole when the wiperarm is at the side of the upper reversal position relative to thereference position, at least either the first magnetism detectionelement or the second magnetism detection element being locatedvis-à-vis the first magnetic pole when the wiper arm is at the side ofthe lower reversal position relative to the reference position.
 4. Thedevice according to claim 3, wherein the first magnetism detectionelement is located vis-à-vis the boundary of the first magnetic pole andthe second magnetic pole when the wiper arm passes the referenceposition.
 5. The device according to claim 3, wherein both the firstmagnetism detection element and the second magnetism detection elementare located vis-à-vis the first magnetic pole when the wiper arm is atthe lower reversal position.
 6. The device according to claim 3, whereina wiper arm stored position is arranged below the lower reversalposition and the first magnetism detection element is located vis-à-visthe first magnetic pole and the second magnetism detection element islocated vis-à-vis the second magnetic pole when the wiper arm is at thestored position.
 7. The device according to claim 3, wherein, when thewiper arm stops between the upper reversal position and the lowerreversal position in operation, it is always started to move toward thereference position at the time of restarting.
 8. The device according toclaim 6, wherein, when the wiper arm stops at a position other than thestored position, the wiper arm is always started to move toward thereference position at the time of restarting.
 9. The device according toclaim 3, characterized by further comprising: a sensor for detecting therotary angle of the rotary shaft, which sensor starts detecting therotary angle of the rotary shaft at the time when the wiper arm ispositioned at the reference position.
 10. An electric motor with a speedreduction mechanism including a motor main body having a rotary shaftand a speed reduction mechanism for reducing the number of revolutionsof the rotary shaft and transmits the revolutions to an output shaft,comprising: a first magnetism detection element arranged so as to belocated vis-à-vis a predetermined position of the output shaft when thewiper arm is at a reference position; a second magnetism detectionelement arranged at a position separated from the first magnetismdetection element by a predetermined angle; and a sensor magnet arrangedat the output shaft and having a first magnetic pole and a secondmagnetic pole arranged in a peripheral direction and showing differentpolarities, both the first and second magnetism detection elements beinglocated vis-à-vis the second magnetic pole when the wiper arm is at oneside relative to the reference position, at least either the firstmagnetism detection element or the second magnetism detection elementbeing located vis-à-vis the first magnetic pole when the wiper arm is atthe other side relative to the reference position.
 11. A method forcontrolling a wiper device, driving a wiper arm to reciprocate betweenan upper reversal position and a lower reversal position for a wipingoperation, wherein a reference position arranged between the upperreversal position and the lower reversal position; a lower limitposition for mechanically restricting the operation of the wiper arm,arranged below the stored position; and, when the wiper arm stops inoperation, it is always started to move toward the lower limit positionat the time of restarting.
 12. A method for controlling a wiper device,driving a wiper arm to reciprocate between an upper reversal positionand a lower reversal position for a wiping operation, wherein areference position arranged between the upper reversal position and thelower reversal position; a stored position for holding the wiper arm atrest when the wiper arm is stopped, arranged below the lower reversalposition; a lower limit position for mechanically restricting theoperation of the wiper arm, arranged below the stored position; and,when the wiper arm stops between the upper reversal position and thereference position in operation, it is always started to move toward thereference position at the time of restarting; when the wiper arm stopsbetween the reference position and the stored position in operation, itis started to move either toward the reference position or toward thelower limit position at the time of restarting.
 13. A method forcontrolling a wiper device, driving a wiper arm to reciprocate betweenan upper reversal position and a lower reversal position for a wipingoperation, wherein a stored position for holding the wiper arm at restwhen the wiper arm is stopped, arranged below the lower reversalposition; a lower limit position for mechanically restricting theoperation of the wiper arm, arranged below the stored position; and,when the wiper arm is driven to reciprocate between the lower reversalposition and the stored position, it is moved to the lower limitposition for operation in each go and return cycle.
 14. A method forcontrolling a wiper device, driving a wiper arm to reciprocate betweenan upper reversal position and a lower reversal position for a wipingoperation, wherein a reference position arranged between the upperreversal position and the lower reversal position; a stored position forholding the wiper arm at rest when the wiper arm is stopped, arrangedbelow the lower reversal position; a lower limit position formechanically restricting the operation of the wiper arm, arranged belowthe stored position; and, when the wiper arm is driven to reciprocatebetween the lower reversal position and the stored position and if thewiper arm is driven toward the side of the reference position beyond thelower reversal position, it is moved to the lower limit position.
 15. Amethod for controlling a wiper device, driving a wiper arm by means of amotor to reciprocate between an upper reversal position and a lowerreversal position for a wiping operation and controlling the operationof the wiper device by detecting the wiper arm position by means of thecount value of the pulse signal output as a result of the rotary motionof the motor, wherein a reference position for resetting the count valueof the pulse signal to a reference value, arranged between the upperreversal position and the lower reversal position; a stored position forholding the wiper arm at rest when the wiper arm is stopped, arrangedbelow the lower reversal position; a lower limit position formechanically restricting the operation of the wiper arm and causing thecount value of the pulse signal to show a predetermined value, arrangedbelow the stored position; and, when the wiper arm stops in operationbetween the upper reversal position and the reference position, it isalways started to move toward the reference position at the time ofrestarting and the count value of the pulse signal is reset to thereference value as the wiper arm passes the reference position; when thewiper arm stops in operation between the reference position and thestored position, it is started either toward the reference position orthe lower limit position at the time of restarting and the count valueof the pulse signal is reset to the reference value or the predeterminedvalue as the wiper arm passes the reference position or arrives at thelower limit position, whichever appropriate.
 16. A method forcontrolling a wiper device, driving a wiper arm by means of a motor toreciprocate between an upper reversal position and a lower reversalposition for a wiping operation and controlling the operation of thewiper device by detecting the wiper arm position by means of the countvalue of the pulse signal output as a result of the rotary motion of themotor, wherein a reference position for resetting the count value of thepulse signal to a reference value, arranged between the upper reversalposition and the lower reversal position; a stored position for holdingthe wiper arm at rest when the wiper arm is stopped, arranged below thelower reversal position; a lower limit position for mechanicallyrestricting the operation of the wiper arm and causing the count valueof the pulse signal to show a predetermined value, arranged below thestored position; and, when the wiper arm is driven to reciprocatebetween the lower reversal position and the stored position, it is movedto the lower limit position for operation in each go and return cycleand the count value of the pulse signal is reset to the predeterminedvalue in response to the arrival of the wiper arm to the lower limitposition.
 17. A method for controlling a wiper device, driving a wiperarm by means of a motor to reciprocate between an upper reversalposition and a lower reversal position for a wiping operation andcontrolling the operation of the wiper device by detecting the wiper armposition by means of the count value of the pulse signal output as aresult of the rotary motion of the motor, wherein a reference positionfor resetting the count value of the pulse signal to a reference value,arranged between the upper reversal position and the lower reversalposition, a stored position for holding the wiper arm at rest when thewiper arm is stopped, arranged below the lower reversal position; alower limit position for mechanically restricting the operation of thewiper arm and causing the count value of the pulse signal to show apredetermined value, arranged below the stored position; and, when thewiper arm is driven to reciprocate between the lower reversal positionand the stored position and if the count value of the pulse signal showsa value indicating as if the wiper arm were positioned at the side ofthe reference position beyond the lower reversal position, the wiper armis moved to the lower limit position and the count value of the pulsesignal is reset to the predetermined value in response to the arrival ofthe wiper arm to the lower limit position.
 18. The device according toclaim 4, wherein both the first magnetism detection element and thesecond magnetism detection element are located vis-à-vis the firstmagnetic pole when the wiper arm is at the lower reversal position. 19.The device according to claim 4, wherein a wiper arm stored position isarranged below the lower reversal position and the first magnetismdetection element is located vis-à-vis the first magnetic pole and thesecond magnetism detection element is located vis-à-vis the secondmagnetic pole when the wiper arm is at the stored position.
 20. Thedevice according to claim 5, wherein a wiper arm stored position isarranged below the lower reversal position and the first magnetismdetection element is located vis-à-vis the first magnetic pole and thesecond magnetism detection element is located vis-à-vis the secondmagnetic pole when the wiper arm is at the stored position.
 21. Thedevice according to claim 4, wherein, when the wiper arm stops betweenthe upper reversal position and the lower reversal position inoperation, it is always started to move toward the reference position atthe time of restarting.
 22. The device according to claim 5, wherein,when the wiper arm stops between the upper reversal position and thelower reversal position in operation, it is always started to movetoward the reference position at the time of restarting.
 23. The deviceaccording to claim 6, wherein, when the wiper arm stops between theupper reversal position and the lower reversal position in operation, itis always started to move toward the reference position at the time ofrestarting.
 24. The device according to claim 4, characterized byfurther comprising: a sensor for detecting the rotary angle of therotary shaft, which sensor starts detecting the rotary angle of therotary shaft at the time when the wiper arm is positioned at thereference position.
 25. The device according to claim 5, characterizedby further comprising: a sensor for detecting the rotary angle of therotary shaft, which sensor starts detecting the rotary angle of therotary shaft at the time when the wiper arm is positioned at thereference position.
 26. The device according to claim 6, characterizedby further comprising: a sensor for detecting the rotary angle of therotary shaft, which sensor starts detecting the rotary angle of therotary shaft at the time when the wiper arm is positioned at thereference position.
 27. The device according to claim 7, characterizedby further comprising: a sensor for detecting the rotary angle of therotary shaft, which sensor starts detecting the rotary angle of therotary shaft at the time when the wiper arm is positioned at thereference position.
 28. The device according to claim 8, characterizedby further comprising: a sensor for detecting the rotary angle of therotary shaft, which sensor starts detecting the rotary angle of therotary shaft at the time when the wiper arm is positioned at thereference position.